Re: Old is expired (was: Re: Is cryopreservation a solution?)

The Low Golden Willow (
Thu, 2 Oct 1997 18:40:58 -0700 (PDT)

On Oct 1, 10:57pm, Damien Broderick wrote:

} *continue* as a benefit. (On the other hand, we set out with a limited if
} Vast immunity repertoire, and the little bastards who breed in us keep
} changing their formula, so the simple passage of time might be enough to
} make oldsters vulnerable to Widowmaker '99 - but that doesn't explain these

I'm not sure what you're saying here. Considering that we only have
100,000 active genes, as far as anyone can tell, we start out with a
rather small immunity repertoire. But lymphocytes -- the antigen
specific white blood cells -- actually have their genes rearranged as
they split from a stem cell, thus making them the only somatic cells
which do not have the same genome as all the other cells. Estimates of
their possible diverity range from 10^8-10^11 for B cells (blood/serum
antibodies) and 10^15-10^18 for some other branch (which by elimination
should be the T cells (which kill infected or tumorous cells) but I
could have forgotten something.) In the latter case there are obviously
rather more possibilities than cells in the body. More time to evolve
is no inherent advantage on the pathogens side.

The entire specific immune system is an excellent example of applied
evolution; many new lymphocytes die due to inability to recognize MHC
molecules or ability to recognize self-antigens. B cells can change
their own genomes to an effort to develop higher affinity receptors,
although I forget what stage that occurs in. Between all this, the way
neurons hook up, and Hofstadter's work on creativity, I'm rather tempted
to say that life is an evolutionary fractal.

} after 50 fertile years. But we know there are snazzy mechanisms for
} healing sick DNA and other damage - a different point, granted - because
} our gonadal DNA is 3 billion years old and not a day the worse for it (same
} homeobox sequences, often enough - highly conservative). Aside from those

Homeobox sequences might be conserved not because they get special
repair mechanisms, but because mutants of those genes thoroughly disable
their hosts, possibly killing them in development. That seems the
simpler explanation for highly conserved sequences -- we depend on them
too closely, so any variants die.

And the whole point is that much DNA is not very highly conserved, and
is "a day the worse for it". That's how we evolved from prokarya.

Merry part,
-xx- Damien R. Sullivan X-) <*>

I'll dance upon your grave a twelvemonth and a day
I'll do as much for you, as any maiden may.
I'll make you rue the very day you were born
I'm a bonnie brown girl...